Production of aromatics in the presence of nitrogen compounds



Feb- 3, 1959 G. R. DONALDSON ET AL 2,372,492

PRODUCTION OF' AROMATICS IN THE PRESENCE OF' NITROGEN COMPOUNDS Filed March 29, 195e United States George R. Donaldson, North Riverside, and Vladimir Haensel, Hinsdale, Ill., assignors to Universal Gil Products Company, Des Plaines, Ill., a corporation of Delaware Application March 29, 1956, Serial No. 574,893

7 Claims. (Cl. 260-668) This invention relates to a method of processing a select petroleum fraction for the purpose of producing aromatics in substantially greater concentrations than have heretofore been considered possible.

It is known that certain narrow boiling range petroleum fractions contain relatively large amounts of naphthenes or cycloparatiins such as cyclohexane, methylcyclohexane, dimethylcyclohexane and ethylcyclohexane and some aromatic compounds, as well as straight chain or slightly branched chain parains. These petroleum fractions may be derived from virgin petroleum stocks or may be derived from stocks that have previously been subjected to catalytic or thermal conversion processes. It is also well known that these fractions may be subjected to various aromatizing pro-cesses in which the naphthene or cycloparaiiin hydrocarbons are converted into aromatics. One example of such a conversion is the dehydrogenation of cyclohexane to benzene. In other methods -for the production of aromatics, full boiling range gasolines are reformed to convert the cycloparaflins to aromatics and, by dehydrocyclization, converting straight chain or slightly branched chain parains into aromatics.

The most commonly used method of recovering the aromatic compounds from the thus processed hydrocar- `bon mixture, which contains the unconverted cyclohexanes and associated open chain paranic hydrocarbons, is by liquid-liquid solvent extraction with selective solvents, such as liquid sulfur dioxide, furfural, phenol, alkyl phenols, glycols, etc., or by liquid vapor extraction using those selective solvents which have boiling points sufficiently higher than the bubble point or boiling temperature of the hydrocarbon mixture to avoid being carried over in the raffinate to any appreciable extent.

These methods will produce an aromatic product which usually contains benzene and toluene, as well as equilibrium co-ncentrations of ortho, paraand metaxylenes and ethylbenzene. If an entire pre-xylene fraction which contains the dimethyl cyclohexanes and ethylcyclohexane is subjected to a reforming process to convert these naphthenes into aromatics, the resultant aromatic product will contain the aforementioned ortho, paraand meta-xylenes and ethylbenzene, in equilibrium concentrations, the ratios of components being approximately 20: 20:45: l5, respectively. I

Although the aforementioned aromatic products which comprise mixtures of several aromatics could be fractionally distilled to separate pure individual compounds fractionation of such mixtures is difficult because of the closeness of the boiling points ofthe pure components, as shown in the following Table l; consequently in order to obtain the pure components, elaborate and expensive fractionating equipment would be required.

TABLE I Compound: B. P., F; Ortho-xylene 289 Meta-xylene 283 Para-xylene 281 Ethylbenzene 277 In our invention two aromatic product streams are obtained, one of which contains a mixture of para-, metaand some ortho-xylene and theother contains primarily ethylbenzene with a small amount of ortho-xylene. The ortho-xylene can be fractionally distilled from both streams, since it is the highest boiling C8 aromatic; the fractionation leaves behind mixtures of metaand paraxylenes in one case and ethylbenzene in the other. The para-xylene may be separated from the meta-xylene by other known means, such as fractional crystallization.

Examination of the boiling points of the C8 naphthenes normally present in petroleum hydrocarbons indicates that itis possible to separate a pre-xylene fraction into two cuts, one of which will contain compounds ultimately producing para, metaand ortho-xylene while the other will contain compounds ultimately converted into ethylbenzene and some ortho-xylene. In the following Table I, the C8 cyclohexane compounds are listed, together with their boiling points and the aromatic compounds which by dehydrogenation they may be converted into, the data clearly indicating that such a separation is feasible. t

Thus by prefactionating the napthene-containing charging stock into two cuts, one containing most of the paraand metaand some ortho-xylene-producing cyclohexane derivatives and the other containing most of the ethylbenzene and some ortho-xylene-producing cyclohexane derivatives, it is possible by means of the present aromatization process, to produce two product streams, one containing primarily metaand para-xylenes and the other containing primarily ethylbenzene. The orthoxylene in both streams can be removed by fractionation or by other suitable separating means. The para-xylene may be separated from the meta-xylene by known methods, such as fractional crystallization. It can be readily observed that the large difference in the boiling points of ortho-xylene and ethylbenzene makes, a separation thereof by fractionation much simpler to accomplish, than their separation when large amounts of metaand para-xylenes are also present. It would be expected that by removing the metaand para-xylene-producing cyclohexane derivatives the ethylbenzene and the ortho-xyleneproducing cyclohexane derivatives would tend to produce the aforementioned equilibrium mixture of ortho, paraand meta-xylenes and ethylbenzene upon aromatization and, in fact, by using the usual aromatization process conditions, the equilibrium mixture is produced; however, by exercising rigid control of the aromatization reaction in accordance with the process of this invention, the establishment of equilibrium concentrations of the indicated aromatics in the product stream can be prevented. This is an entirely unexpected result. Thus, by means of this invention a product containing aromatics in very high concentrations can be produced and the aromatics will be present in a mixture from which they may easily be separated. One means of control whereby the aforementioned results are obtained is by restricting the aromatization to -membered ring naphthenes only and eliminating the dehydrogenation of the S-mernbered ring naphthenes. Under certain conditions, some. dehydrogenation of the S-membered ring. naphthen'es may be obtained; however, the product from. such particular type of dehydrogenation should be of the desired aromatic structure, that is, either a mixture of metaparaand ortho-xylenes on the one hand, or amixture of ethylbenzene and ortho-xylene on the other. The control of the aromatization reaction to limit the conversion to the reaction of 6-mernbered ring naphthenes is effected by control of the space velocity variable of the reaction. lt has been found that ethylcyclohexane, for example, will dehydrogenate readily to produce ethylbenzene at space velocities of 50, 25, and 8 with noside reactions. However, at a space velocity of 4 some disproportionation tends to take place, thereby reducing the ultimate ethylbenzene yield. Furthermore, it has been found that the reaction of parafns to produce aromatics through the dehydrocyclization reaction will also take place if the space velocity is too low. Thus, in order to avoid the formation of other than the desired aromatic isomer products, high space velocities are utilized.

It is realized that the original straight run fraction may contain an appreciable amount of aromatic hydrocarbons. Since the presence of these materials would interfere withthe fractionation and subsequent purification of this product, it is preferred to extract the aromatics from the charging stock prior to the fractionation and subsequent dehydrogenation. These originally present aromatic hydrocarbons may be removed by any of the suitable processes herein mentioned.

Another means of restricting the aromatization to that of 6-membered ring naphthenes only and eliminating the dehydrogenation of the S-membered ring naphthenes is by the addition of a small amount of aA basic nitro-gen compound to the charging stoclr which reduces the iso-merizing capacity of the catalyst and thereby prevents S-membered ring naphthenes from being converted into aromatics. Furthermore, the same addition of basic nitrogen compound will prevent isomerization of the resulting aromatic hydrocarbons, such as the isomerization of ortho-xylene into para-xylene.

The nitrogenous feedV stock additive utilized in the present process to reduce isomerization of the charge stock includes those compounds that exhibit basic properties under the conditions prevailing in the aromatization zone, including compounds having basic properties under normal conditions and which do not decompose or undergo alteration in the reaction zone except by reaction with the catalyst. Still other utilizable additives include compounds that may or may not exhibit basic properties under normalv conditions, but which in the reaction zone are decomposed or altered to compounds that exhibit basicity. Typical representative basic nitrogen compounds, useful as additives to the feed stock are the halogen-free, nitrogen-containingV compounds, such as ammonia, hydrazine, the nitrogen oxides; nitrates and nitrites, includingl sodium and potassium nitrate, and the corresponding alkali metal and ammonium nitrites; aliphatic and aryl nitro compounds,y such as nitro-methane, dinitro-methane,y and nitro-benzene; the nitroso compounds, the primary, secondary, and tertiary aliphatic and aryl amines, such as tertiary butyl` amine and aniline; quaternary ammonium compounds such as quaternary ammonium sulfate; the heterocyclic organic nitrogen compounds such as pyrrole, pyridine, quinaline and derivatives thereof, as well as other classes of compounds having the foregoing properties. Ammonia is an example of a compound that exhibits basic properties under normal conditions and which also exhibits basic properties under the conversion conditions in the reaction zone. On the other hand, nitromethane is an example of a compound which does not exhibit any substantial basic properties under normal conditions but which under the conditions in the reaction zone is converted in part to ammonia.

The amount of nitrogen compound required to obtain the desired suppression of the aromatization of S-membered ring naphthenes can be determined by simple experimentation, One simple method is by observing the total temperature drop through the reactor. lf too much of the nitrogen compound is used, dehydrogenation of the i.S-membered ring compounds will be suppressed and in this case the temperature drop through the reactor will be less than when all of the -membered ring compounds are converted to aromatics. Another simple method of determining the correct amount of compound to be added is to observe the composition of the product streams and after comparing the total conversion to aromatics to the cyclohexane content of the feed stock, adjusting the amount of additive to obtain the desired conversion.

ln a broad embodiment the present invention relates to a process for producing aromatic hydrocarbons which comprises fractionatiug a hydrocarbon mixture comprising dimethylcyclohexane and ethylcyclohexane hydrocarbons into two fractions of different boiling ranges, one fraction containing l,4-dimethylcyclohexane, 1,3-dimethylcyclohexane and some 1,2-dimethylcyclohexane and the other fraction containing ethylcyclohexane and some 1,2- dimethylcyclohexane, separately contacting each fraction at aromatizing conditions withan aromatizing catalyst in the presence vof a basic halogen-free nitrogen-containing compound to thereby inhibit aromatization of 5 membered ring naphthenes.

Another embodiment of the present invention relates to a process for producing ethylbenzene which comprises fractionating a hydrocarbonrnixture comprising dimethylcyclohexane and ethylcyclohexane hydrocarbons into two fractions of different boiling. ranges, one fraction containing l,ll-dimethylcyclohexane, 1,3-dimethylcyclohexane and some 1,2-dimethylcyclohexane and the other fraction containing ethylcyclohexane and some 1,2-dimethylcycl0- hexane and separately subjecting each fraction to contact at a temperature of from abo-ut 600 to about 1000" F., at a pressure of from about 50 to about 1000 p. s. i. and at a'weight hourly space velocity of from about 4 to about 50 with an aromatizing catalyst comprising platinum supported o-n alumina and in the presence of an additive to the charge stock comprising a basic nitrogen-containing compound and fractionating each resulting mixture to yield high purity aromatic products.

The aromatization reaction is preferably effected at a temperature within the range of from about 600 to about 1000" F., at a pressure of from about 50 to about 1000 p. s. i. and a weight hourly space velocity of from about 4 to about 50.

The aromatization catalyst co-mprising platinum supported on alumina and which may also contain combined halogen, as hereinafter described is utilized in the present process to effect the desired selective conversion of -membered ring to their corresponding aromatic hydrocarbons and is capable of such aromatization in the presence of the additive herein provided to inhibit simultaneous aromatization of S-mernbered ring naphthenes. The platinum may be composited with the carrier in any suitable manner. A particularly satisfactory method is to commingle a chloroplatinic acid solution with a support and then subject the composite to a calcination treatment. The amount of platinum composited with the support may vary from about 0.01 to about 1% by weight on the dry basis. In preparing the preferred platinum-aluminahalogen catalyst, the halogen is incorporated in the alumina prior to the addition of the platinum compound. One method of adding the halogen, generally the preferred procedure, isto add the halogen to the alumina in theformof an acid, such as hydrogen uoride, hydrogen -present platinum-containing aromatization catalyst, is subjected to a combined desulfurization-hydrogenation step wherein the material is first desulfurized and subsequently hydrogenated in order to convert the aromatic components present in the initial charging stock to naphthenes. The hydrogen for such desulfurization and hydrogenation is obtained from the aromatization zone, containing a net excess of hydrogen, the desulfurization-hydrogenation step being carried out in two separate contacting zones which may be in separate reactors or may be incorporated into a single vessel using countercurrent flow of charging stock and hydrogen.

Thus a modified preferred embodiment of the present invention provides for treating the entire pre-xylene fraction by the method which comprises passing the oil stream downwardly through a desulfurization contacting zone having a sulfur-resistant catalyst and contacting the latter in the presence of hydrogen passing upwardly therethrough, countercurrently to the descending gasoline fraction to thereby effect a substantial desulfurization of the gasoline fraction, passing the resulting substantially desulfurized gasoline fraction from said zone to a hydrogenation zone wherein the fraction is contacted with a hydrogenation catalyst in the presence of an upwardly, and countercurrently flowing hydrogen stream obtained from the aromatization section, withdrawing a hydrogen sulfide-containing hydrogen stream from the upper portion of the desulfurization zone and withdrawing a hydrogenated sulfur-free gasoline fraction from the lower portion of the dehydrogenation zone. The contacting zones may be in separate reacto-rs or may be incorporated into a single vessel.

The catalyst in the first stage of contact for effecting the hydro-desulfurization of the gasoline fraction stream is a sulfur-resistant catalyst and may be a sulfide of Group VIA or Group VIII of the periodic system or a mixture of the same, either as such or supported on an inert carrier which may be composed of alumina, silica, diatomaceous earth, and the like. For example, molybdenum sulfide on activated alumina or cobalt thio-molybdate supported on alumina or sulfidedplatinumor palladium supported on alumina may comprise a desirable catalyst in the first or hydrodesulfurization stage of contact. The pressure in this process may be in the range of from about 100 to about 1000 p. s. i. g. and temperatures of from about 500 to about 900 F., but preferably of the order of about 700 to about 850 F., may be maintained therein. VAn excess amount of hydrogen should be present and the feed rate of the oil stream or weight hourly space velocity defined as the weight of hydrocarbon charged per hour per weight of catalyst in the reaction zone is desirably within the range of from about 0.2 to

vabout 20.

In the second or hydrogenation stage of contact, a catalyst such as a supported metal of Group VIII of the periodic system may be employed. For example, metallic nickel, platinum or palladium supported on alumina may comprise a desirable catalyst. The temperature in the second stage of contact may be somewhat lower than that in the first stage, generally from about 350 to about 700 F. and preferably of the order of about 600 F. The' optimum operating temperature will increase as the hydrogen pressure is increased. As in the first stage of contact, excess hydrogen should be present and the rate of charging the feed stock may be as hereinbefore set forth for the first stage of contact. While countercurrent methods of desulfurization and hydrogenation are prefrred, it is`understood that the invention is not limited thereto and these conversions may be effected in any suitable manner, including concurrent iiow arrangements.

The novelty and utility of the present invention is further described in the accompanying fiow diagram, illustrating a particularY method of conducting the process which incorporates several specific embodiments of the invention. For simplification, equipment such as valves, pumps, heat exchangers, and similar appurtenances have been omitted in the drawing. These are well known and are not essential to the understanding of the description. As a further means of simplifying the description of the fiow, the diagram will be described with reference to a particular charge stock, catalyst, and arrangement of steps, with no intention, however, of limiting the invention thereto. Figure l illustrates one flow arrangement suitable for effecting the process of this invention. Figure 2 illustrates another embodiment of the invention, showing in greater detail the countercurrent desulfurization and hydrogenation method of contact as described aforesaid.

Referring now to Figure l of the drawing, a 230 to 280 F. boiling range gasoline fraction is charged into line 1 and transferred by means of pump 2 into line 3 which directs the feed stock into extraction zone 4 wherein the aromatic hydrocarbons are extracted from the naphthenic and paratiinic hydrocarbon components of the feed stocks. This extraction of aromatic hydrocarbons from the naphthenic and parafiinic hydrocarbons may be made either by batch or continuous processes although from the standpoint of efficiency a countercurrent fiow extraction method is preferable. Details of the batch and countercurrent flow procedures are generally well known and need not be enlarged upon here, since they form no special feature of the present invention.

The aromatic products are withdrawn from zone 4 through line 5 for subsequent separation and purification. The rafhnate comprising essentially the naphthenic and paraffinic hydrocarbons is withdrawn from zone 4 through line 6 and directed into fractional distillation column 7 wherein it is separated into a low boiling frac`- tion having a boiling range from 230 to 250 F., removed through line 8, and a high boiling fraction, boiling from 250 to 280 F. which is removed through line 9. As in the usual methods of fractional distillation, the low boiling fraction recovered through line 8 directed through a cooler and the resulting condensate accumulates in a receiver, with some of the cooled light fraction used as refiux to the fractionating column. The high boiling pre-xylene fraction recovered from column 7 through line 9 is directed to heater 10 wherein it is heated to the desired aromatization temperature and it is then di1ected,'together with recycle hydrogen from line 19, through line 11 into aromatizing reactor 12.

An aromatizing catalyst is retained within reactor 12 and the heavy pre-xylene" fraction is passed therethrough in either downward flow, as illustrated, or in upward fiow by means not illustrated. In the case herein illustrated the catalyst is deposited as a fixed bed in reactors 12 and 29, but it is to be emphasized that the process may'also be effected in other types of catalyst-feed stock methods of contact, such as fiuidized, suspensoid and moving bed types of operation inwhich the catalyst is intimately contacted with the feed stock.

Aromatized products are withdrawnv from zone 12 through line 13 and passed through cooler 14 and line 15 into receiver 16. In receiver 16 substantially all the hydrogen is separated from the liquid product. The hydrogen in receiver 16 is withdrawn therefrom through line 17 by means of compressor 18 and is thereafter discharged into line 19 which conveys the stream into re-` actor 12. Excess hydrogen is withdrawn from the system through line 19A. The hydrogen in line 19 may be into reactor 12. It is also possible to effect the aromatizing under such conditions that. recycle hydrogen is unnecessary and in :such a process the recycle gas system hereinbefore described may be eliminated. The excess hydrogen withdrawn from the system through line 19A may be used as the hydrogen supply in line 53 of Figure 2.

The liquid product in receiver 16 which is rich in ortho-xylene and ethylbenzene but which also contains some unconverted naphthenic and parainic hydrocarbons is withdrawn through line 20 andv directed to extractio-n zone '21, in which a mixture of aromatic hydrocarbons rich in ortho-xylene and ethylbenzene is extracted from unconverted naphthenic and parainic hydrocarbons. The unconverted naphthenic and paraffinic hydrocarbons are withdrawn from zone 21 through line 22 and may be blended into gasoline products or they may be recycled by well known means, not illustrated, and reintroduced into fractionator 7 or into aromatic extraction unit 4. The aromatic hydrocarbons in zone 21 are Withdrawn through line 23 and directed into fractionator 24 wherein an overhead product rich in ethylbenzene is withdrawn through line 25 and a bottoms product rich in ortho-xylene is withdrawn through line 26. These product streams may be subjected to further treatment to recover the individual products in a purer form.

In a like manner thelow boiling .prexylene fraction in line 8 is directed to heater 27 which raises the temperature of this stream to a level suticient to effect the desired aromatization thereof, and is then directed in yeither upward or downward flow through line 28 into aromatizing reactor 29, along with the recycle hydrogen supplied from line 36. Aromatizing reactor 29 contains a fixed bed of aromatization catalyst, such as a composite of platinum on an alumina support containing a fixed halogen or halide such as chlorine and/or liuorine.

Aromatized products are withdrawn from zone 29 through line 30 and passed through cooler 31 and line 32 .into receiver 33. In receiver 33 substantially all the hydrogen is separated from the liquid product. The hydrogen in receiver 33 is withdrawn through line 34, thereafter picked up by compresso-r 35 and discharged into line 36 from which it is directed into reactor 29. Excess hydrogen is withdrawn from the system through line 36A. The hydrogen in line 36 may be passed through a heater, not illustrated, wherein it is raised to the desired aromatizing temperature before being directed into reactor 29. It is also possible to effect the desired aromatization under such conditions that recycle hydrogen is unnecessary and in such a process the recycle gas system as hereinbefore described may be eliminated. The excess hydrogen withdrawn fro-m the system through line 36A may also be used as a source of hydrogen for line 53 of Figure 2.

The liquid product in receiver 33 which is rich in paraand meta-xylenes but which also contains some unconverted naphthenic and parainic hydrocarbons is withdrawn through line 37 and directed to extraction zone 38 in which the mixture of aromatic hydrocarbons rich in metaand para-xylene is extracted from unconverted naphthenic and paraflinic hydrocarbons. The unconverted naphthenic and parainic hydrocarbons are withdrawn as raffinate from zone 3S through line 39 and may be means not illustrated be blended into gasoline products or they may be recycled and reintroduced into fractionator 7 or aromatic extraction unit 4. The aromatic hydrocarbons in zone 3S are withdrawn through line 40 and directed into fractionator 41 wherein the overhead product rich in metaand para-xylenes is withdrawn through line 42 and` the bottoms product which is rich in ortho-xylene is withdrawn through line 45. These product streams may-be subjected to further treatment to recover the individual products in a purer form, if desired.v The usual; method ot' separating the paraxylene from the meta-Xylene is by fractional crystallization but other means, known Yto the art may also be employed.

Referring now to Figure 2 of the diagram, illustrating a modified, preferred embodiment. of the present invention a two-stage hydrogenation operation is thereby provided wherein the oil stream flows countercurrently to a hydrogen stream in each of the two steps of the catalytic hydrogenation process thus illustrated. To illustrate by reference to a specific charge stock, a 230 to 280 F. boiling range gasoline 4fraction is directed into line 44, picked up by pump 45' and passed through line 46 into heater 47 wherein it is raised to a temperature sufficient to effect hydrogenation thereof and it is then directed through line 48 into desulfurization zone 49 wherein it is contacted with a sulfur-resistant desulfurization catalyst at desulfurizing conditions in the presence of hydrogen. The latter hydrogen stream desirably moves upwardly through the catalyst, counter-current to the descending gasoline fraction, thereby at least partially saturating and substantially desulfurizing the charging stock. The resulting mixed hydrogen sulfide-hydrogen stream is withdrawn from zone 49 through line 55. The gasoline fraction is withdrawn from zone 49 through line 50 and is passed together with hydrogen into hydrogenation reactor 51, therein contacting a hydrogenating catalyst at hydrogenation reaction conditions, the hydrogen being charged into the lower portion of the reactor and thus allowed to flow upwardly through the catalyst, countercurrently to the descending oil stream, thereby substantially hydrogenating the latter. The desulfurized and hydrogenated gasoline fraction is withdrawn from zone 5l through line 52 for introduction into fractionator 7 of Figure l. The hydrogen supply in line S3 which is introduced into hydrogenation zone 5i can be obtained from the aromatization section of the process, as aforesaid, from lines 19A and/ or line 36A of Figure 1. When using the latter modification of the invention, the unconverted naphthenic and paraffinic hydrocarbons withdrawn from zones 38 or '21 through lines 39 or 22, respectively, of Figure 2 may be returned to the hydrogenation step through lines. 44 or 50, since these streams will usually also contain small amounts of. aromatic components.

The following examples are given to illustrate the present invention, but are not to be interpreted for the purpose of unduly limiting the generally broad scope of the invention necessarily in accordance therewith.

Example l A gasoline fraction boiling within the range of from 230 to 278 F. was fractionated to give a light pre-xylene sub-fraction and a heavy pre-xylene sub-fraction. The heavy pre-xylene fraction boiling Within the range of from 254 to 278 F. was hydrogenated over a nickelkieselguhr catalyst to saturate the aromatic compounds. This hydroxylene was fractionated into fo-ur cuts and each cut was separately reformed with a platinum-alumina-halogen catalyst at 8 liquid hourly space velocity, at a pressure of 350 p. s. i. g. and in the presence of sufficient hydrogen to provide a 3 to 1 hydrogen to hydrocarbon molar ratio, the reactor inlet temperature to the hydrogenation zone being 878 F.

The products were distilled to provide a 248 to 302 F. fraction which contains essentially all of the Xylenes and ethylbenzene formed in the aromatization process. These fractions were examined to determine the ethylbenzene content and a calculation was made of the percent of ethylbenzene recovered in each fraction. Table III lists the following: in column l the temperature ranges of the several cuts selected for aromatization, in column 2 the percent of ethylbenzene in the 248 to 302 F. fraction recovered from the product, and in column 3 the percentages of ethylbenzene produced, compared to the amount that could .be produced had the entire 254-27 8 F. .beenaromatized at thesame spacevelocity.

TABLE III F. Percent Percent Ethylbenzene Ethylbenzene Itis thus seen from the above example that much higher purities of ethylbenzene, than the equilibrium purity of may be obtained by exercising a rigid control of the aromatization reaction.

g Example I1 g Example III The 254278 F. cut of Example I was aromatized at the same conditions as designated in Example I; however, in the` present conversion, 0.5% by Weight of pyridine was added tothe charging stock. An inspection of the product showed an ethylbenzene content of 81.8%, the recovery compared to the conversion in which the total 254-278 F. fraction was aromatized under the conditions of Example I was 92.0%. Thus, while the pyridine inhibited the conversion of the S-mernbered ring naphthenes into aromatics as shown by the higher concentration, it did not affect the conversion of the 6membered ring naphthenes into the corresponding aromatics.

Example IV In order to more decisively demonstrate the eifect of a nitrogen-containing additive on the isomerizing and aromatizing ability of the aromatizing catalyst on 6-.membered ring naphthenes as compared to S-membered ring naphthenes, two separate fractions, one of which consists of 100% cyclohexane and the other of which consists of 100% methylcyclopentane were each individually and each in admixture with a small quantity of sec-butyl amine additive separately passed over a so-called Platforming aromatization catalyst capable of effecting both aromatization and isomerization reactions, including the isomerization of alkylcyclopentanes to benzene and its derivatives. The Platforming catalyst is a highly active catalytic composite of platinum on a carrier comprising alumina containing xed halogen in the form of iluorine and chlorine, the catalyst containing 0.05% by weight of platinum and 0.15% and 0.2% by weight, respectively, of chlorine and liuorine combined with the alumina in the form of a complex or a salt therewith. lThe feed stocks were charged, as closely as practicable at the same temperature and under otherwise similar reaction conditions into the upper portion of a Platforming reactor in order to provide data capable of being compared and evaluated on the same basis of comparison. The indicated feed stock were charged into the top of the reactor, being a vertical tubular column containing a fixed bed of the above-indicated catalyst, a product stream cornprising conversion products of the process being removed from the bottom of the reactor, cooled and the liquid product condensed therefrom and collected in a receiver vessel. The following table presents the pertinent operating data, analysis of the product and the yields and conversions obtained in the above process.

r in the absence of the amine additive.

TABLE IV Comparative conversion of methylcyclopentane and cyclo' hexane at aromatizing conditions and the effect thereon of including a basic nitrogen-containing compound in the feed MCPl CHZ With With- With With- SBA2 out SBA out SBA SBA Aromatization Reactor Temperature,

F 496 496 495 496 Liquid Hourly Space Velocity 2.0 2.0 4. 5 4. 5 Pressure, p. s. 1. g 200 200 200 200 i12/Hydrocarbon, Mole/Mole. 4 4 4 4 Lquid Product:

Yield, Wt. Percent of Charge 95.8 94.1 95.4 95.5

Benzene, Wt. Percent of Product. 30 55 69. U 69. 5

Benzene, Wt. Percent of Charge.. 28. 7 61. 7 65. 8 66. 4

Gas Product:

Analysis- Note:

1 Methylcyclcpentane. 1 seolbutylarnine.

3 Cyclohexane.

It will be noted from the results indicated in the above table that when methylcyclopentane (that is, a 5-membered ring naphthene) is subjected to aromatizing conditions in the presence of an aromatizing catalyst (the above indicated Platforming catalyst, containing acidacting halogen ions) the C5 naphthene undergoes substantial conversion to benzene (approximately 55%), the catalyst being capable of eiecting both the isomerization of methylcyclopentane to a -membered ring naphthene andV also the aromatization of the resulting cyclohexane into benzene by dehydrogenatio-n of the C6 ring. However, when sec-butyl amine is added to the methylcyclopentane charge and the resulting mixture passed over the Platforming catalyst at aromatizing conditions, the conversion of the 5-membered ring methylcyclopentane into benzene is reduced to approximately one-half the conversion of the same methylcyclopentane charge into benzene Thus, the amine has a profound eiect on the isomerizing capacity of the catalyst in its ability to convert C5 ring naphthenes into C6 ring aro-matic hydrocarbons.

The above results relating to the aromatization of methylcyclopentane are to be contrasted with the results of passing cyclohexane over an aromatizing catalyst at aromatizing conditions with and without the identical amine additive utilized in the similar conversion of methylcyclopentane. It will be noted from the results indicated above in Table IV that the sec-butyl amine has little or no effect on the conversion of a C6 ring naphthene, such as cyclohexane, into benzene when included as an additive in the cyclohexane charge stock. Thus, the additive which was effective for limiting the isomerization of a C5 ring' naphthene into a C6 ring aromatic hydrocarbon has no effect on the degree of conversion of a C6 ring naphtha into a C6 ring aromatic.

This application is a continuation-in-part of our copending application Serial No. 299,571, tiled July 18, 1952, now abandoned.

We claim as our invention:

1. In a process wherein a hydrocarbon mixture containing S-membered ring naphthenes and -rnembered ring naphthenes is contacted at aromatizing conditions with a platinum-containing aromatizing catalyst, the improvement which comprises adding to the hydrocarbon mixture a halogen-free, nitrogen-containing compound having basic properties at said conditions in suicient amount to suppress dehydrogenation of the 5-membered ring naphthenes and to prevent isomerization of the arch4 matic hydrocarbons resulting from the aromatization of the -membered ring naphthenes. 2. A process for producing aromatic hydrocarbons which comprises fractionating a hydrocarbon mixture comprising dimethylcyclohexane and ethylcyclohexane hydrocarbons into two fractions of different boiling ranges, one fraction containing 1,4-dimethylcyclohexane, 1,3-dimethylcyclohexane and some 1,2dimethy1cyc1ohexane and the other fraction containing ethylcyclohexane and some 1,2-dimethylcyclohexane, adding to each fraction a suicient amount of a basic halogen-free, nitrogencontaining compound to inhibit aromatization of 5-membered ring naphthenes, and separately contacting each of said fractions containing added nitrogen compound with a platinum-containing aromatizing catalyst at aromatizing conditions. n

3. A process for Yproducing aromatic hydrocarbons which comprises subjecting a petroleum fraction boiling within the gasoline boiling range and containing C6 aromatic hydrocarbons to hydrogenation at hydrogenating reaction conditions sutlcient to -convert the aromatic hydrocarbon components to naphthenes, thereafter fractionating the resulting hydrogenated petroleum fraction into two fractions of different boiling ranges, one fraction containing 1,4-dimethylcyclohexane, 1,3-dimethylcyc1ohexane and 1,2-dimethylcyclohexane and the other fraction containing ethylcyclohexane and 1,2-dimethylcyclohexane, adding to cach fraction a sucient amount of a basic, halogen-free, nitrogen-containing compound to inhibit aromatization of S-membered ring naphthenes, and r separately contacting each of said fractions containing added notrogen compound with a platinum-containing aromatizing catalyst at aromatizing conditions.

4. A process for producing aromatic hydrocarbons which comprises fractionating a hydrocarbon mixture comprising dimethylcyclohexane and ethylcyclohexane hydrocarbons into two fractions of different boiling ranges, one fraction containing 1,4-dimethylcyclohexane, 1,3-dimetbylcyclohexane and some 1,2-dirnethy1cyclo- '12 hexane and the other fraction containing ethylcyclohexane and some 1,2-dimethylcyc1ohexane, separately subjecting each fraction to contact at a temperature of from about 600 to about 1000" F., a pressure of from about 50 to about 1,000 p. s. i., and a weight hourly space velocity of from about 4 to about 50 with a platinum-containing aromatizing catalyst in the presence ofaV basic, halogenfree, nitrogen-'containing compound, said compound having been added to each fraction in sutlcient amount to inhibit aromatization of the 5-membered ring naphthenes, and fractionating the resulting materials to yield high purity aromatic products.

5. The process of claim 1 further characterized in that said aromatizing catalyst comprises alumina containing from about 0.01 to about 1% platinum.

6. The process of claim 1 further characterized in that said aromatzing catalyst comprises alumina containing from about 0.01 to about 1% platinum and from about 0.1 to about 8% by weight of halogen.

7. The process of claim 1 further characterized in that said nitrogen-containing compound is a normally liquid aliphatic amine.

References Cited in the file of this patent UNITED STATES PATENTS 2,184,235 Groll et al. Dec. 19, 1939 2,282,231 Mattox May 5, 1942 2,611,736 Haensel Sept. 23, 1952 2,653,175 Davis Sept. 22, 1953 2,723,946 Donaldson Nov. 15, 1955 2,742,515 Stuart Apr. 17, 1956 2,784,241 Holm Mar. 5, 1957 FOREIGN PATENTS 590,548 Great Britain July 22, 1947 OTHER REFERENCES Millseet al.: Jour. Amer. Chem. Soc., vol. 72, April 1950, pp. 1554-1560. 

1. IN A PROCESS WHEREIN A HYDROCARBON MIXTURE CONTANING 5-MEMBERED RING NAPHTENES AND 6-MEMBERED RING NAPHTHENES IS CONTACTED AT AROMATIZING CONDITIONS WITH A PLASTINUM-CONTAINING AROMATIZING CATALYST, THE IMPROVEMENT WHICH COMPRISES ADDING TO THE HYDROCARBON MIXTURE A HALOGEN-FREE, NITROGEN-CONTAINING COMPOUND HAVING BASIC PROPERITIES AT SAID CONDITIONS IN SUFFICIENT AMOUNT TO SUPPRES DEHYDROGENATION OF THE 5-MEMBERED RING NAPHTENES AND TO PREVENT ISOMERIZATION OF THE AROMATIC HYDROCARBONS RESULTING FROM THE AROPMATIZATION OF THE 6-MEMBERED RING NATHTENES. 